Medical imaging methods and systems use a variety of imaging modalities. Each modality can be characterized by its typical spatial and temporal resolution. For example, the following table shows typically achievable spatial and temporal resolution values of several known imaging modalities:
SpatialresolutionTemporal resolution(per axis)(three-dimensional frameModality[mm]refresh rate) [Hz]Ultrasound120-30Single positron emission510computerized tomography(SPECT)Positron emission tomography310(PET)Computerized tomography0.5-110(CT)Magnetic resonance imaging0.5-110(MRI)
Some methods and systems use radio frequency (RF) based imaging. For example, U.S. Pat. No. 6,490,471, whose disclosure is incorporated herein by reference, describes a single-frequency three-dimensional (3-D) microwave tomographic device capable of imaging a full scale biological object. The device includes code-division software, which cooperates with a microwave patch system to enable superficial imaging of biological systems. A cluster of antennas and transceivers is used to provide microwave tomography (MWT) and electrical impedance tomography (EIT) integrated in a single 3-D microwave system for examining the biological object from a number of views in real-time.
PCT International Publication WO 03/003907, which is incorporated herein by reference, describes a system for microwave imaging via space-time beam-forming. Microwave signals are transmitted from multiple antenna locations into an individual to be examined. Backscattered microwave signals are received at multiple antenna locations, to provide received signals from the antennas. The received signals are processed in a computer to remove the skin interface reflection component of the signal at each antenna. The corrected signal data is processed by a beam-former. The beam-former is scanned over a plurality of different locations in the individual by changing time shifts, filter weights and time-gating of the beam-former process. The output power may be displayed as a function of scan location, with regions of large output power corresponding to significant microwave scatterers such as malignant lesions.
U.S. Pat. No. 6,448,788, whose disclosure is incorporated herein by reference, describes a method and apparatus for microwave imaging of an inhomogeneous target, in particular of biological tissue. The method compensates for the interactions between active and non-active antennas. Measured electric field data is processed in magnitude and phase form, so that unwrapped phase information may be used directly in the image reconstruction. Initial finite element measurements and calculations are used to determine the perimeter dimensions of the target being examined.
U.S. Pat. No. 6,253,100, whose disclosure is incorporated herein by reference, describes a method for imaging an object, such as a diseased human heart or bone, in a non-transparent medium, such as the human body. The method involves placing an array of transmitters and receivers in operational association with the medium. The transmitters generate a harmonic or pulse primary electromagnetic (EM) field, which propagates through the medium. The primary field interacts with the object to produce a scattered field, which is recorded by the receivers. The scattered EM field components measured by the receivers are applied as an artificial EM field to generate a backscattering EM field. Cross power spectra of the primary and backscattering fields or cross correlation between these fields produce a numerical reconstruction of an EM hologram. The desired properties of the medium, such as conductivity or dielectric permittivity, are then derived from this hologram.